Method and apparatus for predicting and restoring a video signal using palette entry

ABSTRACT

Provided is a method for decoding a video signal. Such a method may include constructing a palette map for a current block encoded in a palette mode, the palette map comprising at least one palette entry and a map index that identifies the palette entry, deriving a palette index of the current block on a sample-by-sample basis, and reconstructing a current sample based on an escape mode if a value of the palette index relating to the current sample of the current block is equal to the number of palette entries constituting the palette map of the current block, wherein the escape mode is a method of restoring a sample value based on a signaled palette escape value, without using a palette entry of the constructed palette map.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage Patent Application of PCTInternational Patent Application No. PCT/KR2015/010717 (filed on Oct.12, 2015) under 35 U.S.C. § 371, which claims priority to Korean PatentApplication No. 10-2014-0141557 (filed on Oct. 20, 2014), the teachingsof which are incorporated herein in their entireties by reference.

TECHNICAL FIELD

The present invention relates to a method and a device for processing avideo signal.

BACKGROUND ART

Demands for high-resolution, high-quality images such as High Definition(HD) images and Ultra High Definition (UHD) images have recentlyincreased in various fields of applications. As video data has a higherresolution and higher quality, the video data is larger in amount thantraditional video data. Therefore, if video data is transmitted on anexisting medium such as a wired/wireless wideband circuit or stored inan existing storage medium, transmission cost and storage cost increase.To avert these problems encountered with higher-resolution,higher-quality video data, high-efficiency video compression techniquesmay be used.

There are a variety of video compression techniques includinginter-picture prediction in which pixel values included in a currentpicture are predicted from a picture previous to or following thecurrent picture, intra-picture prediction in which pixel values includedin a current picture are predicted using pixel information in thecurrent picture, and entropy encoding in which a short code is assignedto a more frequent value and a long code is assigned to a less frequentvalue. Video data may be compressed effectively and transmitted orstored, using such a video compression technique.

Along with the increasing demands for high-resolution videos, demandsfor three-dimensional (3D) video content as a new video service havebeen increasing. A video compression technique for effectively providingHD and UHD 3D video content is under discussion.

DISCLOSURE Technical Problem

An object of the present invention is to provide a method and apparatusfor predicting or restoring a video signal based on a palette mode inencoding/decoding a video signal.

An object of the present invention is to provide a method and apparatusfor constructing a palette map of a block to be encoded/decoded inencoding/decoding a video signal.

An object of the present invention is to provide a method and apparatusfor deriving a palette index of a block to be encoded/decoded inencoding/decoding a video signal.

Technical Solution

A method of decoding a video signal according to the present inventionincludes constructing a palette map for a current block encoded in apalette mode, the palette map comprising at least one palette entry anda map index that identifies the palette entry, deriving a palette indexin units of samples of the current block, and reconstructing a currentsample based on an escape mode if a value of the palette index relatingto the current sample of the current block is equal to the number ofpalette entries constituting the palette map of the current block. Theescape mode is a method of restoring a sample value based on a signaledpalette escape value, without using a palette entry of the constructedpalette map.

In the method of decoding a video signal according to the presentinvention, the palette entry comprises at least one of a predictedpalette entry or a signaled palette entry, and the predicted paletteentry means a palette entry reused in the current block among paletteentries included in a palette map of a previous block, and the signaledpalette entry indicates a palette entry not included in a palette map ofa previous block among the palette entries used by the current block.

In the method of decoding a video signal according to the presentinvention, the palette index is derived using at least one of an indexmode (INDEX MODE) or a copy mode (COPY MODE), and the index mode (INDEXMODE) is a method of deriving a palette index based on encoded paletteindex information, and the copy mode (COPY MODE) is a method of derivinga palette index of the current sample using a palette index of aneighboring sample.

In the method of decoding a video signal according to the presentinvention, the escape mode is adaptively used based on at least one ofthe number of palette entries in a palette map of the current block or aflag indicating whether the current block includes at least one sampleencoded in the escape mode.

An apparatus of decoding a video signal according to the presentinvention includes a restoring unit for constructing a palette map for acurrent block encoded in a palette mode, deriving a palette index inunits of samples of the current block, and reconstructing a currentsample based on an escape mode if a value of the palette index relatingto the current sample of the current block is equal to the number ofpalette entries constituting the palette map of the current block. Thepalette map comprises at least one palette entry and a map index thatidentifies the palette entry, and the escape mode is a method ofrestoring a sample value based on a signaled palette escape value,without using a palette entry of the constructed palette map.

In the apparatus of decoding a video signal according to the presentinvention, the palette entry includes at least one of a predictedpalette entry or a signaled palette entry, and the predicted paletteentry means a palette entry reused in the current block among paletteentries included in a palette map of a previous block, and the signaledpalette entry indicates a palette entry not included in a palette map ofa previous block among the palette entries used by the current block.

In the apparatus of decoding a video signal according to the presentinvention, the restoring unit derives the palette index using at leastone of an index mode (INDEX MODE) or a copy mode (COPY MODE), and theindex mode (INDEX MODE) is a method of deriving a palette index based onencoded palette index information, and the copy mode (COPY MODE) is amethod of deriving a palette index of the current sample using a paletteindex of a neighboring sample.

In the apparatus of decoding a video signal according to the presentinvention, the escape mode is adaptively used based on at least one ofthe number of palette entries in a palette map of the current block or aflag indicating whether the current block includes at least one sampleencoded in the escape mode.

A method of encoding a video signal according to the present inventionincludes constructing a palette map for a current block encoded in apalette mode, the palette map comprising at least one palette entry anda map index that identifies the palette entry, deriving a palette indexin units of samples of the current block, and reconstructing a currentsample based on an escape mode if a value of the palette index relatingto the current sample of the current block is equal to the number ofpalette entries constituting the palette map of the current block. Theescape mode is a method of restoring a sample value based on a signaledpalette escape value, without using a palette entry of the constructedpalette map.

In the method of encoding a video signal according to the presentinvention, the palette entry comprises at least one of a predictedpalette entry or a signaled palette entry, and the predicted paletteentry means a palette entry reused in the current block among paletteentries included in a palette map of a previous block, and the signaledpalette entry indicates a palette entry not included in a palette map ofa previous block among the palette entries used by the current block.

In the method of encoding a video signal according to the presentinvention, the palette index is derived using at least one of an indexmode (INDEX MODE) or a copy mode (COPY MODE), and the index mode (INDEXMODE) is a method of deriving a palette index based on encoded paletteindex information, and the copy mode (COPY MODE) is a method of derivinga palette index of the current sample using a palette index of aneighboring sample.

In the method of encoding a video signal according to the presentinvention, the escape mode is adaptively used based on at least one ofthe number of palette entries in a palette map of the current block or aflag indicating whether the current block includes at least one sampleencoded in the escape mode.

An apparatus of encoding a video signal according to the presentinvention includes a restoring unit for constructing a palette map for acurrent block encoded in a palette mode, deriving a palette index inunits of samples of the current block, and reconstructing a currentsample based on an escape mode if a value of the palette index relatingto the current sample of the current block is equal to the number ofpalette entries constituting the palette map of the current block, thepalette map comprises at least one palette entry and a map index thatidentifies the palette entry, and the escape mode is a method ofrestoring a sample value based on a signaled palette escape value,without using a palette entry of the constructed palette map.

In the apparatus for decoding a video signal according to the presentinvention, the restoring unit derives the palette index using at leastone of an index mode (INDEX MODE) or a copy mode (COPY MODE), and theindex mode (INDEX MODE) is a method of deriving a palette index based onencoded palette index information, and the copy mode (COPY MODE) is amethod of deriving a palette index of the current sample using a paletteindex of a neighboring sample.

In the apparatus for decoding a video signal according to the presentinvention, escape mode is adaptively used based on at least one of thenumber of palette entries in a palette map of the current block or aflag indicating whether the current block includes at least one sampleencoded in the escape mode.

Advantageous Effects

According to the present invention, it is possible to improve theefficiency of prediction or restoration of a block to be encoded/decodedbased on a palette mode.

According to the present invention, the pallet entry encoding/decodingefficiency can be improved by deriving the palette map of the block tobe encoded/decoded from the palette map of the previous block.

According to the present invention, a palette index of a block to beencoded/decoded can be efficiently derived based on an index mode or acopy mode.

According to the present invention, the compression efficiency can beimproved by encoding the palette index using the binary vector based onthe run encoding.

According to the present invention, the sample values of the block to beencoded/decoded can be restored based on the escape mode, so that thesamples out of the palette entry range can be efficientlyencoded/decoded.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a video encoding apparatusaccording to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating an video decoding apparatusaccording to an embodiment of the present invention.

FIG. 3 illustrates a method of restoring a current block based on apalette mode according to an embodiment of the present invention.

FIG. 4 illustrates a method of restrictively signaling of a reuse flag(previous_palette_entry_flag) according to an embodiment of the presentinvention.

FIG. 5 illustrates a method of signaling a reuse flag in the form of abinary vector based on a run encoding, according to an embodiment of thepresent invention.

FIG. 6 illustrates a method for restrictively obtaining a reuse flagbased on a last entry flag (last_previous_entry_flag), according to anembodiment of the present invention.

FIG. 7 illustrates a method of deriving a palette index of a currentblock based on palette index information and a palette index runaccording to an embodiment of the present invention.

FIG. 8 illustrates a method of deriving a palette index of a currentblock based on palette index information and a palette index run whenthe palette map of the current block is composed of two palette entries.

FIG. 9 illustrates a scan order in the palette mode according to anembodiment of the present invention.

FIG. 10 illustrates a method of determining the number of paletteentries used by a current block according to an embodiment of thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A method of decoding a video signal according to the present inventionincludes constructing a palette map for a current block encoded in apalette mode, the palette map comprising at least one palette entry anda map index that identifies the palette entry, deriving a palette indexin units of samples of the current block, and reconstructing a currentsample based on an escape mode if a value of the palette index relatingto the current sample of the current block is equal to the number ofpalette entries constituting the palette map of the current block. Theescape mode is a method of restoring a sample value based on a signaledpalette escape value, without using a palette entry of the constructedpalette map.

In the method of decoding a video signal according to the presentinvention, the palette entry comprises at least one of a predictedpalette entry or a signaled palette entry, and the predicted paletteentry means a palette entry reused in the current block among paletteentries included in a palette map of a previous block, and the signaledpalette entry indicates a palette entry not included in a palette map ofa previous block among the palette entries used by the current block.

In the method of decoding a video signal according to the presentinvention, the palette index is derived using at least one of an indexmode (INDEX MODE) or a copy mode (COPY MODE), and the index mode (INDEXMODE) is a method of deriving a palette index based on encoded paletteindex information, and the copy mode (COPY MODE) is a method of derivinga palette index of the current sample using a palette index of aneighboring sample.

In the method of decoding a video signal according to the presentinvention, the escape mode is adaptively used based on at least one ofthe number of palette entries in a palette map of the current block or aflag indicating whether the current block includes at least one sampleencoded in the escape mode.

An apparatus of decoding a video signal according to the presentinvention includes a restoring unit for constructing a palette map for acurrent block encoded in a palette mode, deriving a palette index inunits of samples of the current block, and reconstructing a currentsample based on an escape mode if a value of the palette index relatingto the current sample of the current block is equal to the number ofpalette entries constituting the palette map of the current block. Thepalette map comprises at least one palette entry and a map index thatidentifies the palette entry, and the escape mode is a method ofrestoring a sample value based on a signaled palette escape value,without using a palette entry of the constructed palette map.

In the apparatus of decoding a video signal according to the presentinvention, the palette entry includes at least one of a predictedpalette entry or a signaled palette entry, and the predicted paletteentry means a palette entry reused in the current block among paletteentries included in a palette map of a previous block, and the signaledpalette entry indicates a palette entry not included in a palette map ofa previous block among the palette entries used by the current block.

In the apparatus of decoding a video signal according to the presentinvention, the restoring unit derives the palette index using at leastone of an index mode (INDEX MODE) or a copy mode (COPY MODE), and theindex mode (INDEX MODE) is a method of deriving a palette index based onencoded palette index information, and the copy mode (COPY MODE) is amethod of deriving a palette index of the current sample using a paletteindex of a neighboring sample.

In the apparatus of decoding a video signal according to the presentinvention, the escape mode is adaptively used based on at least one ofthe number of palette entries in a palette map of the current block or aflag indicating whether the current block includes at least one sampleencoded in the escape mode.

A method of encoding a video signal according to the present inventionincludes constructing a palette map for a current block encoded in apalette mode, the palette map comprising at least one palette entry anda map index that identifies the palette entry, deriving a palette indexin units of samples of the current block, and reconstructing a currentsample based on an escape mode if a value of the palette index relatingto the current sample of the current block is equal to the number ofpalette entries constituting the palette map of the current block. Theescape mode is a method of restoring a sample value based on a signaledpalette escape value, without using a palette entry of the constructedpalette map.

In the method of encoding a video signal according to the presentinvention, the palette entry comprises at least one of a predictedpalette entry or a signaled palette entry, and the predicted paletteentry means a palette entry reused in the current block among paletteentries included in a palette map of a previous block, and the signaledpalette entry indicates a palette entry not included in a palette map ofa previous block among the palette entries used by the current block.

In the method of encoding a video signal according to the presentinvention, the palette index is derived using at least one of an indexmode (INDEX MODE) or a copy mode (COPY MODE), and the index mode (INDEXMODE) is a method of deriving a palette index based on encoded paletteindex information, and the copy mode (COPY MODE) is a method of derivinga palette index of the current sample using a palette index of aneighboring sample.

In the method of encoding a video signal according to the presentinvention, the escape mode is adaptively used based on at least one ofthe number of palette entries in a palette map of the current block or aflag indicating whether the current block includes at least one sampleencoded in the escape mode.

An apparatus of encoding a video signal according to the presentinvention includes a restoring unit for constructing a palette map for acurrent block encoded in a palette mode, deriving a palette index inunits of samples of the current block, and reconstructing a currentsample based on an escape mode if a value of the palette index relatingto the current sample of the current block is equal to the number ofpalette entries constituting the palette map of the current block, thepalette map comprises at least one palette entry and a map index thatidentifies the palette entry, and the escape mode is a method ofrestoring a sample value based on a signaled palette escape value,without using a palette entry of the constructed palette map.

In the apparatus for decoding a video signal according to the presentinvention, the restoring unit derives the palette index using at leastone of an index mode (INDEX MODE) or a copy mode (COPY MODE), and theindex mode (INDEX MODE) is a method of deriving a palette index based onencoded palette index information, and the copy mode (COPY MODE) is amethod of deriving a palette index of the current sample using a paletteindex of a neighboring sample.

In the apparatus for decoding a video signal according to the presentinvention, the escape mode is adaptively used based on at least one ofthe number of palette entries in a palette map of the current block or aflag indicating whether the current block includes at least one sampleencoded in the escape mode.

MODE FOR CARRYING OUT THE INVENTION

The present invention may be changed and modified variously and beillustrated with reference to different exemplary embodiments, some ofwhich will be described and shown in the drawings. However, theseembodiments are not intended for limiting the invention but areconstrued as including includes all modifications, equivalents andreplacements which belong to the spirit and technical scope of theinvention. Like reference numerals in the drawings refer to likeelements throughout.

Although the terms first, second, etc. may be used to describe variouselements, these elements should not be limited by these terms. Theseterms are used only to distinguish one element from another element. Forexample, a first element could be termed a second element and a secondelement could be termed a first element likewise without departing fromthe teachings of the present invention. The term “and/or” includes anyand all combinations of a plurality of associated listed items.

It will be understood that when an element is referred to as being“connected to” or “coupled to” another element, the element can bedirectly connected or coupled to another element or interveningelements. On the contrary, when an element is referred to as being“directly connected to” or “directly coupled to” another element, thereare no intervening elements present.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “include” and/or“have,” when used in this specification, specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof.

Hereinafter, exemplary embodiments of the invention will be described indetail with reference to the accompanying drawings. Like referencenumerals in the drawings refer to like elements throughout, andredundant descriptions of like elements will be omitted herein.

FIG. 1 is a block diagram illustrating a video encoding apparatusaccording to an embodiment of the present invention.

Referring to FIG. 1, the video encoding apparatus 100 includes a picturedividing unit 110, prediction units 120 and 125, a transform unit 130, aquantization unit 135, a reordering unit 160, an entropy encoding unit165, an inverse quantization unit 140, an inverse transform unit 145, afilter unit 150, and a memory 155.

Each of the elements shown in FIG. 1 is shown independently to representdifferent characteristic functions in the video encoding apparatus, anddoes not mean that each element is composed of separate hardware or onesoftware configuration unit. That is, the elements are independentlyarranged for convenience of description, wherein at least two elementsmay be combined into a single element, or a single element may bedivided into a plurality of elements to perform functions. It is to benoted that embodiments in which some elements are integrated into onecombined element and/or an element is divided into multiple separateelements are included in the scope of the present invention withoutdeparting from the essence of the present invention.

Some elements are not essential to the substantial functions in theinvention and may be optional constituents for merely improvingperformance. The invention may be embodied by including onlyconstituents essential to embodiment of the invention, except forconstituents used to merely improve performance. The structure includingonly the essential constituents except for the optical constituents usedto merely improve performance belongs to the scope of the invention.

The picture dividing unit 110 may divide an input picture into at leastone processing unit. Here, the processing unit may be a prediction unit(PU), a transform unit (TU) or a coding unit (CU). The picture dividingunit 110 may divide one picture into a plurality of combinations of CUs,PUs and TUs and encode the picture by selecting one combination of CUs,PUs and TUs on the basis of a predetermined criterion (for example, acost function).

For example, one picture may be partitioned into a plurality of CUs. Arecursive tree structure, such as a quad tree structure, may be used topartition a picture into CUs. A CU, for which a picture or a CU of amaximum size may be as root, may be partitioned into sub-coding unitswith as many child nodes as the partitioned CUs. A CU which is notpartitioned any more in accordance with a predetermined limitation is aleaf node. That is, assuming that a CU may be partitioned into quadrantsonly, a single CU may be partitioned into at most four different CUs.

In the embodiments of the invention, a CU may be used to refer to notonly a unit of encoding but also a unit of decoding.

A PU may be partitioned into at least one square or rectangular formwith the same size in a CU. For PUs partitioned from a same CU, a PU mayhave different shape and/or size from another PU.

When a PU for intra prediction is generated based on a CU and the CU isnot a minimum CU, the CU may be subjected to intra prediction withoutbeing partitioned into plural PUs (N×N).

The prediction units 120 and 125 may include an inter prediction unit120 to perform inter prediction and an intra prediction unit 125 toperform intra prediction. The prediction units 120 and 125 may determinewhich of inter prediction and intra prediction is performed on a PU, andmay determine specific information (for example, an intra predictionmode, a motion vector, and a reference picture) of the determinedprediction method. Here, a processing unit on which prediction isperformed may be different from a processing unit for which a predictionmethod and specific information thereon are determined. For example, aprediction method and a prediction mode may be determined for each PU,while prediction may be performed for each TU. A residual value(residual block) between a generated predicted block and an originalblock may be input to the transform unit 130. Further, prediction modeinformation, motion vector information and the like used for predictionmay be encoded along with the residual value by the entropy encodingunit 165 and be transmitted to the decoding apparatus. When a specificencoding mode is used, the original block may be encoded and transmittedto the decoding apparatus without generating a prediction block by theprediction units 120 and 125.

The inter prediction unit 120 may predict a PU based on information onat least one picture among a previous picture of a current picture and asubsequent picture of a current picture. In some cases, the interprediction unit 120 may predict a PU based on information of a partiallyencoded region in the current picture. The inter prediction unit 120 mayinclude a reference picture interpolation unit, a motion predictionunit, and a motion compensation unit.

The reference picture interpolation unit may be supplied with referencepicture information from the memory 155 and generate pixel informationless than or equal to an integer pixel on a reference picture. In thecase of luma pixels, a DCT-based 8-tap interpolation filter with avariable filter coefficient may be used to generate pixel informationless than or equal to an integer pixel in a unit of a ¼ pixel. In thecase of chroma pixels, a DCT-based 4-tap interpolation filter with avariable filter coefficient may be used to generate pixel informationless than or equal to an integer pixel in a unit of a ⅛ pixel.

The motion prediction unit may perform motion prediction on the basis ofthe reference picture interpolated by the reference pictureinterpolation unit. Various methods, such as a full search-based blockmatching algorithm (FBMA), a three-step search (TSS) algorithm and a newthree-step search (NTS) algorithm, may be used to calculate a motionvector. A motion vector has a motion vector value in the unit of a ½ or¼ pixel on the basis of an interpolated pixel. The motion predictionunit may predict a current PU using different motion prediction methods.Various methods, such as skip mode, merge mode, and advanced motionvector prediction (AMVP) mode, intra block copy mode, etc. may be usedas the motion prediction method.

The intra prediction unit 125 may generate a PU on the basis ofinformation on a reference pixel neighboring to a current block. When areference pixel is a pixel for which inter prediction has been performedbecause a block neighboring to the current PU is a block for which interprediction has been performed, information on a reference pixel in theblock for which inter prediction has been performed may be replaced withinformation on a reference pixel in a block for which intra predictionhas been performed. That is, when a reference pixel is not available,information on the unavailable reference pixel may be replaced withinformation on at least one reference pixel of the available referencepixels.

A prediction mode of intra prediction includes a directional predictionmode in which reference pixel information is used according to aprediction direction and a non-directional prediction mode in whichinformation on direction is not used in performing prediction. A modefor predicting luma information and a mode for predicting chromainformation may be different from each other. Further, intra predictionmode information used to obtain luma information or predicted lumasignal information may be used to predict chroma information.

When a PU and a TU have the same size, intra prediction on the PU may beperformed based on a left pixel, an upper-left pixel and an upper pixelof the PU. On the other hand, when a PU and a TU have different sizes,intra prediction may be performed by using reference pixels which aredetermined based on the TU. Intra prediction using N×N partitioning maybe performed only for a minimum CU.

In the intra prediction method, a predicted block may be generated byapplying an adaptive intra smoothing (AIS) filter to the referencepixels according to the prediction mode. Different types of AIS filtersmay be applied to the reference pixels. In the intra prediction method,the intra prediction mode of a current PU may be predicted from an intraprediction mode of a PU neighboring to the current PU. In predicting theprediction mode of the current PU using mode information predicted froma neighboring PU, when the current PU and the neighboring PU have thesame intra prediction mode, information indicating that the current PUand the neighboring PU have the same prediction mode may be transmittedusing predetermined flag information. When the current PU and theneighboring PU have different prediction modes, information on theprediction mode of the current block may be encoded by entropy encoding.

A residual block including residual information may be generated. Theresidual information is a difference between the original block of thePU and the predicted block of a PU generated by the prediction units 120and 125. The generated residual block may be input to the transform unit130.

The transform unit 130 may transform the residual block using atransform method such as Discrete Cosine Transform (DCT), Discrete SineTransform (DST) or KLT. The residual block includes information on theresidual between the PU generated by the prediction units 120 and 125and the original block. A transform method to be used to transform theresidual block may be determined among DCT, DST and KLT on the basis ofthe information on the intra prediction mode of the PU which is used togenerate the residual block.

The quantization unit 135 may quantize values transformed into afrequency domain by the transform unit 130. A quantization coefficientmay be changed depending on a block or importance of an image. Valuesoutput from the quantization unit 135 may be provided to thedequantization unit 140 and the rearrangement unit 160.

The rearrangement unit 160 may rearrange quantized coefficients.

The rearrangement unit 160 may change a two-dimensional (2D) block ofcoefficients into a one-dimensional (1D) vector of coefficients throughcoefficient scanning. For example, the rearrangement unit 125 may changea 2D block of coefficients into a 1D vector of coefficients by scanningfrom DC coefficients to coefficients of a high frequency domain usingzigzag scanning. Vertical scanning for scanning a 2D block ofcoefficients in a vertical and horizontal scanning for scanning a 2Dblock of coefficients in a horizontal direction may be used depending ona size of a TU and an intra prediction mode, instead of zigzag scanning.That is, a scanning method may be selected based on the size of the TUand the intra prediction mode, among zigzag scanning, vertical scanning,and horizontal scanning.

The entropy encoding unit 165 may perform entropy encoding on the basisof the values obtained by the rearrangement unit 160. Various encodingmethods, such as exponential Golomb coding, context-adaptive variablelength coding (CAVLC), or context-adaptive binary arithmetic coding(CABAC), may be used for entropy encoding.

The entropy encoding unit 165 may encode a variety of information, suchas residual coefficient information and block type information on a CU,prediction mode information, partitioning unit information, PUinformation, transfer unit information, motion vector information,reference frame information, block interpolation information andfiltering information from the rearrangement unit 160 and the predictionunits 120 and 125.

The entropy encoding unit 165 may entropy-encode coefficients of a CUinput from the rearrangement unit 160.

The dequantization unit 140 and the inverse transform unit 145dequantize the values which are quantized by the quantization unit 135and inverse-transform the values which are transformed by the transformunit 130. A reconstructed block may be generated by adding the residualvalues to the predicted PU. The residual values may be generated by thedequantization unit 140 and the inverse transform unit 145. Thepredicted PU may be predicted by the motion vector prediction unit, themotion compensation unit, and the intra prediction unit of theprediction units 120 and 125.

The filter unit 150 may include at least one of a deblocking filter, anoffset unit, and an adaptive loop filter (ALF).

The deblocking filter may remove block distortion generated byboundaries between blocks in a reconstructed picture. Whether to applythe deblocking filter to a current block may be determined on the basisof pixels included in several rows or columns of the block. When thedeblocking filter is applied to a block, a strong filter or a weakfilter may be applied depending on a required deblocking filteringstrength. When horizontal filtering and vertical filtering are performedin applying the deblocking filter, the horizontal filtering and verticalfiltering may be performed in parallel.

The offset unit may apply the offset with respect to the original imageto the deblocking filtered image, in units of pixels. A region to whichthe offset may be applied may be determined after partitioning pixels ofa picture into a predetermined number of regions. The offset may beapplied to the determined region in consideration of edge information oneach pixel or the method of applying the offset to the determinedregion.

The ALF may perform filtering based on a comparison result of thefiltered reconstructed image and the original image. Pixels included inan image may be partitioned into predetermined groups, a filter to beapplied to each group may be determined, and differential filtering maybe performed for each group. Information on whether to apply the ALF maybe transferred by each coding unit (CU) and a shape and filtercoefficients of an ALF to be applied to each block may vary. Further, anALF with the same form (fixed form) may be applied to a block regardlessof characteristics of the block.

The memory 155 may store a reconstructed block or picture output fromthe filter unit 150, and the stored reconstructed block or picture maybe supplied to the prediction units 120 and 125 when performing interprediction.

FIG. 2 is a block diagram illustrating a video decoding apparatusaccording an exemplary embodiment of the present invention.

Referring to FIG. 2, the video decoding apparatus 200 may include anentropy decoding unit 210, a rearrangement unit 215, a dequantizationunit 220, an inverse transform unit 225, prediction units 230 and 235, afilter unit 240, and a memory 245.

When a video bitstream is input from the video encoding apparatus, theinput bitstream may be decoded according to an inverse process of thevideo encoding process performed in the video encoding apparatus.

The entropy decoding unit 210 may perform entropy decoding according toan inverse process of the entropy encoding process by the entropyencoding unit of the video encoding apparatus. For example, variousmethods, such as exponential Golomb coding, CAVLC or CABAC, may be usedfor entropy encoding, corresponding to the method used by the videoencoding apparatus.

The entropy decoding unit 210 may decode information associated withintra prediction and inter prediction performed by the encodingapparatus.

The rearrangement unit 215 may perform rearrangement on the bitstreamentropy-decoded by the entropy decoding unit 210 on the basis of therearrangement method of the encoding unit. The rearrangement unit 215may reconstruct and rearrange coefficients of a 1D vector form intocoefficients of a 2D block. The rearrangement unit 215 may be providedwith information on coefficient scanning performed by the encodingapparatus and may perform rearrangement using a method of inverselyscanning the coefficients, on the basis of scanning order performed bythe encoding apparatus.

The dequantization unit 220 may perform dequantization on the basis of aquantization parameter provided from the encoding apparatus and therearranged coefficients of the block.

The inverse transform unit 225 may perform inverse transform performedby the transform unit (that is, inverse DCT, inverse DST or inverse KLT)on a result of quantization performed by the video encoding apparatus.Inverse transform may be performed on the basis of a transfer unitdetermined by the video encoding apparatus. The transform unit 225 ofthe video decoding apparatus may selectively perform the transformscheme (e.g., DCT, DST, KLT) depending on a plurality of informationelements, such as a prediction method, a size of the current block and aprediction direction, etc.

The prediction units 230 and 235 may generate a prediction block on thebasis of information for generating prediction block and information ona previously-decoded block or picture provided. The information forgenerating prediction block may be provided from the entropy decodingunit 210. The information on a previously-decoded block or picture maybe provided from the memory 245

Similarly to the operation of the video encoding apparatus as describedabove, when a PU and a TU have the same size, intra prediction on the PUis performed based on left pixels, an upper-left pixel and upper pixelsof the PU. On the other hand, when a PU and a TU have different sizes,intra prediction may be performed using reference pixels which aredetermined based on the TU. Intra prediction using N×N partitioning maybe used only for a minimum CU.

The prediction units 230 and 235 may include a PU determination unit, aninter prediction unit and an intra prediction unit. The PU determinationunit may receive a variety of information, such as PU information,prediction mode information on an intra prediction method and motionprediction-related information on an inter prediction method, etc. fromthe entropy decoding unit 210, may determine a PU for a current CU. ThePU determination unit may determine which of the inter prediction andthe intra prediction is performed on the PU. An inter prediction unit230 may perform inter prediction on a current PU on the basis ofinformation on at least one picture among a previous picture and asubsequent picture of a current picture including the current PU. Aninter prediction unit 230 may use information necessary for interprediction for the current PU provided from the video encodingapparatus. The inter prediction may be performed on the basis of theinformation of the pre-reconstructed partial region in the currentpicture including the current PU.

In order to perform inter prediction, it may be determined, in an unitof a CU, whether a motion prediction method for a PU included in the CUis a skip mode, a merge mode, an AMVP mode or intra block copy mode.

An intra prediction unit 235 may generate a prediction block on thebasis of pixel information in a current picture. When a PU is a PU forwhich intra prediction is performed, intra prediction may be performedbased on intra prediction mode information on the PU provided from thevideo encoding apparatus. The intra prediction unit 235 may include anAIS (Adaptive Intra Smoothing) filter, a reference pixel interpolationunit, and a DC filter. The AIS filter performs filtering on referencepixels of a current block. The AIS filter may decide whether to applythe filter or not, depending on a prediction mode for the current PU.AIS filtering may be performed on the reference pixels of the currentblock using the prediction mode for the PU and information on the AISfilter provided from the video encoding apparatus. When the predictionmode for the current block is a mode not performing MS filtering, theAIS filter may not be applied.

When the prediction mode for the PU indicates a prediction mode ofperforming intra prediction on the basis of pixel values obtained byinterpolating the reference pixels, the reference pixel interpolationunit may generate reference pixels in a unit of a fractional pixel lessthan an integer pixel (i.e. full pixel) by interpolating the referencepixels. When the prediction mode for the current PU indicates aprediction mode of generating a prediction block without interpolatingthe reference pixels, the reference pixels may not be interpolated. TheDC filter may generate a prediction block through filtering when theprediction mode for the current block is the DC mode.

The reconstructed block or picture may be provided to the filter unit240. The filter unit 240 includes a deblocking filter, an offset unit,and an ALF.

The video encoding apparatus may provide information on whether thedeblocking filter is applied to a corresponding block or picture, andinformation on which of a strong filter and a weak filter is appliedwhen the deblocking filter is used. The deblocking filter of the videodecoding apparatus may be provided with information on the deblockingfilter from the video encoding apparatus and may perform deblockingfiltering on a corresponding block.

The offset unit may apply offset to the reconstructed picture on thebasis of information on an offset type and offset value applied to thepicture in the encoding process.

The ALF may be applied to a CU on the basis of information on whetherthe ALF is applied and ALF coefficient information, etc. provided fromthe encoding apparatus. The ALF information may be included and providedin a specific parameter set.

The memory 245 may store the reconstructed picture or block for use as areference picture or a reference block and may provide the reconstructedpicture to an output unit.

As described above, in the embodiments of the invention, the term“coding unit” is used as an encoding unit for a convenience ofdescriptions. However, the term “coding unit” may be also used as a unitof decoding.

FIG. 3 illustrates a method of restoring a current block based on apalette mode according to an embodiment of the present invention.

In the case of an image including an animation or a graphic, it mayhappen that all or a part of the image is composed of only a specificpixel value. In this case, a method of encoding a specific pixel valueconstituting the area may be used without using an inter prediction orintra prediction method, which is called a palette mode. The palettemode may be applied in a block unit (for example, a coding unit, aprediction unit). For this purpose, flag information (palette_mode_flag)indicating whether the palette mode is used may be signaled on a blockbasis.

Referring to FIG. 3, a palette map for a current block encoded in apalette mode may be constructed (S300).

The palette map may comprise at least one palette entry and a map indexidentifying each palette entry. The palette map of the current block canbe derived from a palette map of the previous block (hereinafterreferred to as a previous palette map). Here, the previous block maymean a block that has been encoded or decoded before the current block.

The palette entry of the current block may comprise at least one of apredicted palette entry or a signaled palette entry. The current blockmay use all or a part of the palette entries used by the previous block.A predicted palette entry may be representative of the palette entryreused in the current block among the palette entries used in theprevious block.

Specifically, the current block may use the same palette map as theprevious block. For this, a flag (palette_share_flag) indicating whetherthe current block uses the same palette map as the previous block may besignaled. Here, the same palette map means that the size of the palettemap (or the number of palette entries included in the palette map) isthe same and the palette entries included in the palette map are thesame. When the value of palette_share_flag is 1, the current block usesthe same palette map as the previous block. When the value of thepalette_share_flag is 0, the current block may use the palette map inwhich at least one of the size of the palette map or the palette entriesincluded in the palette map is different from that of the neighboringblock.

Alternatively, the current block may selectively use some paletteentries of the previous palette map. For this purpose, a flag(previous_palette_entry_flag, hereinafter referred to as a reuse flag)for specifying whether the palette entry is reused may be used.Specifically, the value of the reuse flag is assigned to each of thepalette entries of the previous palette map. The reuse flag(previous_palette_entry_flag [i]) indicates that the palette entrycorresponding to the map index i in the previous palette map is reusedor not. For example, if the value of the reuse flag is 1, the paletteentry corresponding to the map index i in the previous palette map isreused in the palette map of the current block. Otherwise, it is notreused. A palette map of the current block may be constructed byextracting palette entries having a reuse flag equal to 1 from theprevious pallet map and sequentially arranging the palette entries. Thereuse flag may be signaled in the form of a flag encoded for eachpalette entry, or may be signaled in the form of a binary vector basedon a run encoding, which will be described in detail with reference toFIG. 4 to FIG. 6.

In order to selectively use some of the palette entries in the palettemap of the previous block, a re-use variable array(predictor_palette_entry_reuse_flag) for specifying whether the previouspalette entry is reused and a syntax palette_predictor_run_value forspecifying the number of reuse variables equal to 0 between non-zeroreuse variables in the reuse variable array may be used.

In addition, the palette map of the current block may further include asignaled palette entry signaled from the bitstream. Here, the signaledpalette entry includes a palette entry that is not included in theprevious palette map, among the palette entries used by the currentblock.

Referring to FIG. 3, a palette index may be derived according to apredetermined scan order in a sample unit (or pixel unit) of the currentblock (S310).

As the scan order of the present invention, a horizontal scan, avertical scan, a horizontal traverse scan, a vertical traverse scan, orthe like may be used, and this will be described in detail withreference to FIG. 9.

A palette index for the current block may be derived using at least oneof an index mode (INDEX MODE) or a copy mode (COPY MODE).

Here, the index mode (INDEX MODE) may refer to a method of deriving apalette index based on encoded palette index information to specify apalette index used in the current block. The palette index informationhas a value between 0 and (palette size-1), wherein the palette size mayindicate the size of the palette map of the current block or the numberof palette entries constituting the palette map. In the index mode, thevalue of the signaled palette index information through the bit streammay be assigned to the palette index of the current sample. A method ofderiving a palette index based on the index mode will be described indetail with reference to FIGS. 7 and 8.

The copy mode (COPY MODE) may refer to a method of deriving the paletteindex of the current sample using the palette index of the neighboringsample. For example, in the copy mode, the palette index of the currentsample may be predicted based on the palette index of the neighboringsample, or the palette index of the neighboring sample may be copied andset as the palette index of the current sample. Here, a neighboringsample may mean a sample adjacent to the top, bottom, left, or rightside of the current sample. In particular, the neighboring sample may belocated on the same horizontal line or the same vertical line as thecurrent sample.

The copy mode may include at least one of a copy above mode (COPY_ABOVEMODE) in which a palette entry used by a sample adjacent to the upperend of the current sample is used as a palette entry of the currentsample or a copy left mode (COPY_LEFT MODE) in which a palette entryused by a sample adjacent to the left side of the current sample is usedas a palette entry of the current sample. One of the copy above mode orthe copy left mode may be selectively used according to the scan orderof the current block. For example, if the current block uses ahorizontal scan or a horizontal traverse scan, a copy above mode may beused. If the current block uses a vertical scan or vertical traversescan, a copy left mode may be used. In addition, the scan start positionof the current block is not limited to the upper left sample, and othercorner samples (for example, lower-left sample, upper-right sample, andlower-right sample) of the current block may be used as the scan startposition. Therefore, according to the scan order and the scan startposition of the current block, the same palette entry as the sampleadjacent to the upper or left side may be used, or the same paletteentry as the sample adjacent to the lower or right side may be used. Inthis case, the copy mode may further include a copy right mode(COPY_RIGHT MODE) and/or a copy under mode (COPY_UNDER MODE).

Alternatively, regardless of the scan order, one of the copy above modeor the copy left mode may be selectively used. For this purpose, a flag(use_copy_above_flag) specifying the scan mode may be signaled. Theuse_copy_above_flag may be signaled on a slice header, slice segmentheader, or block basis. If the value of use_copy_above_flag is 1, thecopy above mode may be used in the corresponding slice or block, and ifthe value of use_copy_above_flag is 0, the copy left mode may be used inthat slice or block.

A mode identifier (palette_index_mode) for specifying a method ofderiving a palette index for each sample of a current block may be usedto selectively use any one of the palette index modes such as the indexmode and the copy mode described above. Hereinafter a method of derivinga palette index for each sample of a current block is referred to as apalette index mode. For example, if the value of the mode identifier is1, the current sample of the current block uses the copy mode, and ifthe value of the mode identifier is 0, the current sample may use theindex mode.

The mode identifier may be signaled based on a flag(use_one_palette_mode_flag) indicating whether the current block usesonly one pallet index mode. The use_one_palette_mode_flag may besignaled in units of blocks (for example, coding unit, prediction unit).

For example, when the current block uses only one palette index modeaccording to the value of use_one_palette_mode_flag, the mode identifieris not signaled through the bitstream, and the palette index modepre-defined at the video decoding apparatus may be used as the indexmode of the current block. To this end, the value of the mode identifierfor each sample of the current block may be set to 1 or 0.

On the other hand, according to the value of use_one_palette_mode_flag,the current block is not limited to using only one palette index mode,and the mode identifier may be signaled through a bit stream when aplurality of palette index modes are used.

Alternatively, the mode identifier may be signaled based on a flag(palette_above_present_flag) indicating whether at least one sample inthe current block uses the copy mode.

For example, if at least one of the samples in the current block usesthe copy mode according to the value of palette_above_present_flag, themode identifier may be signaled through the bitstream. On the otherhand, when the samples of the current block do not use the copy modeaccording to the value of palette_above_present_flag, the modeidentifier is not signaled through the bitstream, and the palette indexmode pre-defined at the video decoding apparatus is used as the paletteindex mode of the current block. To this end, the value of the modeidentifier for each sample of the current block may be set to zero.

Referring to FIG. 3, a sample of a current block may be restored basedon the palette index derived in step S310 (S320).

Specifically, the sample of the current block may be restored based onthe palette map of the current block configured in step S300 and thepalette index derived in step S310. A palette entry having a map indexof the same value as the derived palette index is extracted from thepalette map of the current block, and then the sample of the currentblock may be restored using the palette entry. For example, the value ofthe palette entry extracted from the palette map may be set to thepredicted value or the restored value of the sample of the currentblock.

However, the value of the derived palette index may be equal to thenumber of palette entries constituting the palette map of the currentblock. In this case, the sample of the current block can be restored byusing the palette entry of the palette map configured in step S300. Thatis, since the map index of the palette map has a value between 0 (thenumber of palette entries−1), the value of the derived palette indexequal to the number of palette entries means that there is no paletteentry corresponding to the derived palette index in the palette mapconfigured in step S300. In this way, when a sample having a paletteindex of the same value as the number of palette entries in the currentblock exists, the sample may be determined to be encoded in an escapemode (ESCAPE MODE). Here, the escape mode may refer to a method ofrestoring a sample value based on a palette escape value that isadditionally signaled, instead of using the palette entry of the palettemap constructed in step S300. Thus, a sample having a palette indexequal to the number of palette entries may be restored using theadditionally signaled palette escape value.

On the other hand, the escape mode may be adaptively used based on atleast one of the number of palette entries in a palette map of thecurrent block or a flag (palette_escape_val_present_flag) indicatingwhether the current block includes at least one sample encoded in theescape mode. A method for determining the number of palette entries usedby the current block will be described later with reference to FIG. 10.Here, If the value of palette_escape_val_present_flag is 1, it may meanthat the current block includes at least one sample encoded in theescape mode. If the value of the palette_escape_val_present_flag is 0,it may mean that the current block does not include the sample encodedin the escape mode.

Specifically, if the number of palette entries for the current block isgreater than zero (e.g., the number of palette entries is one) and thevalue of palette_escape_val_present_flag is 1, at least one sample ofthe current block may be restored based on an escape mode. That is, thesample encoded in the escape mode in the current block may be restoredbased on the additionally signaled palette escape value.

On the other hand, if the number of palette entries related to thecurrent block is greater than 0 and the value ofpalette_escape_val_present_flag is 0, this means that the current blockdoes not include the samples encoded in the escape mode. Thus, thecurrent block is not restored based on the escape mode. In this case,the current block may be restored using the palette map of the currentblock, based on either the index mode or the copy mode. If the number ofpalette entries related to the current block is greater than 0 and thevalue of palette_escape_val_present_flag is 0, only the index mode isused, and thus a mode identifier (palette_index_mode) specifying thepalette index mode may not be signaled. Further, the palette map may becomposed of predicted palette entries and signaled palette entries asshown in FIG. 3, but is not limited thereto, and may be constituted ofdirectly signaled palette entries only.

On the other hand, if the number of palette entries related to thecurrent block is zero, it is not allowed to restore the current blockbased on the escape mode.

The palette_escape_val_present_flag may be encoded and signaled to thevideo decoding apparatus only when the number of palette entries relatedto the current block is greater than zero. Ifpalette_escape_val_present_flag is not signaled, its value may bederived to be zero in the video decoding apparatus.

FIG. 4 illustrates a method of signaling of a reuse flag(previous_palette_entry_flag) according to an embodiment of the presentinvention.

Referring to FIG. 4, the reuse number information(num_previous_palette_entry) related to the palette map of the currentblock may be obtained from the bitstream (S400).

Here, the reuse number information may mean information encoded toindicate the number of palette entries reused as palette entries of thecurrent block among the palette entries of the previous palette map.

A reuse flag (previous_palette_entry_flag [i]) specifying whether or notthe i-th palette entry is to be reused may be obtained from thebitstream (S410).

The reuse flag is signaled by the size of the previous palette map (orthe number of palette entries included in the previous palette map).Here, i corresponds to a map index that identifies the palette entry ofthe previous palette map, and the value of i is in a range 0 to (size ofthe previous palette map−1).

It may be checked whether the value of the reuse flag obtained in stepS410 is 1 (S420).

As a result of checking, if the value of the reuse flag is 1, a variablenumPredPreviousPalette indicating the number of reuse flags equal to 1may be updated (S430). For example, the value of the variablenumPredPreviousPalette may be increased by one.

On the other hand, if the value of the reuse flag is 0, a reuse flag(previous_palette_entry_flag [i+1]) specifying whether to reuse the(i+1)-th palette entry may be obtained from the bitstream (S410) after avalue ‘i’ is incremented by ‘i=i+1’ (S4201).

It is possible to compare whether the variable numPredPreviousPalettevalue increased in step S430 and the reuse number information obtainedin step S400 are the same (S440).

If the variable numPredPreviousPalette is not equal to the numberinformation obtained in step S400, a reuse flag(previous_palette_entry_flag [i+1]) specifying whether to reuse the(i+1)-th palette entry may be obtained from the bitstream (S410) after avalue ‘i’ is incremented by ‘i=i+1’(S4401). However, if the variablenumPredPreviousPalette is equal to the number information obtained instep S400, a palette entry having a map index greater than the i valuemay not be used as a palette entry of the current block. For this, ifthe variable numPredPreviousPalette is equal to the number informationobtained in step S400, the value of i may be derived to be equal to orlarger than the size of the previous palette map. For example, the valueof i may be derived by adding 1 to the size of the previous palette map.Thus, by setting the value of i to be equal to or greater than the sizeof the previous palette map, the reuse flag associated with the (i+1)-thpalette entry may not be signaled.

FIG. 5 illustrates a method of signaling a reuse flag in the form of abinary vector based on a run encoding, according to an embodiment of thepresent invention.

In the present embodiment, it is assumed that the palette map of theprevious block uses eight palette entries having a map index of 0 to 7.

For each of the palette entries of the previous block with index 0 to 7,the video encoding apparatus determines whether the palette entry isreused as a palette entry of the current block. If the palette entry isreused as a palette entry of the current block, the value of the reuseflag for the palette entry may be set to be 1, and otherwise, it may beset to be 0. For example, as shown in FIG. 5, when the palette entriesof 0, 1, 3, and 7 among the palette entries of the previous block arereused as palette entries of the current block and the remaining paletteentries are not reused, a binary vector represented by 11010001 may begenerated.

Then, at least one of the number of 1's in the binary vector (i.e., thenumber of palette entries reused as a palette entry of the current blockin the previous block) or the number of zeros earlier than 1 in thebinary vector is encoded, and then it may be signaled to the videodecoding apparatus. For example, since the number of 1's in the binaryvector is 4, 4 may be encoded as the number of palette entries of theprevious block reused as the palette entry of the current block. Inaddition, the number of zeros preceding the 1 in the binary vector, thatis, 0, 0, 1, and 3, may be sequentially encoded.

The video decoding apparatus may receive, from the video encodingapparatus, at least one of information (num_previous_palette_entry)about the number of palette entries of a previous block reused aspalette entries of the current block or information (palette_entry_run)about the number of zeros preceding the 1 in the binary vector, and thenconstruct a palette map of the current block by using it.

For example, the video decoding apparatus successively extractsinformation (palette_entry_run) about the number of zeros preceding the1 in the binary vector, that is, 0, 0, 1, and 3, from the bitstream. Thebinary vector indicating whether to reuse the palette entry of aprevious block, that is, 11010001 may be restored by using the extractedinformation. When a value of 1 is generated in the process of restoringthe binary vector, the palette entry of the previous block correspondingto the value 1 may be inserted into the palette map of the currentblock. Through this process, a palette map of the current block may beconstructed by selectively reusing some palette entries from the palettemap of the previous block.

FIG. 6 illustrates a method of obtaining a reuse flag in a limitedmanner based on a last entry flag (last_previous_entry_flag) accordingto an embodiment of the present invention.

Referring to FIG. 6, a reuse flag (previous_palette_entry_flag [idx])may be obtained in consideration of the size of the palette map of theprevious block (S600).

The reuse flag may indicate whether the palette entry corresponding tothe current map index idx in the palette map of the previous block isreused as the palette entry of the current block. The reuse flag may beobtained within a range where the current map index idx is smaller thanthe size of the palette map of the previous block (or the number ofpalette entries constituting the palette map of the previous block).

The last entry flag (last_previous_entry_flag) may be obtained based onthe reuse flag obtained in step S600 (S610).

Specifically, if the value of the reuse flag is 1, the last entry flagis extracted from the bitstream, and if the value of the reuse flag is0, the last entry flag is not extracted from the bitstream.

Here, the last entry flag may indicate whether the palette entrycorresponding to the current map index idx is the last palette entry ofthe palette entries of the previous block that are reused as the paletteentry of the current block. For example, if the value of the last entryflag is 1, a palette entry having a map index value greater than thecurrent map index idx is not reused as a palette entry of the currentblock. On the other hand, if the value of the last entry flag is 0, atleast one of the palette entries having the map index value greater thanthe current map index idx may be reused as the palette entry of thecurrent block.

The value of the current map index idx may be updated to be apredetermined value based on the last entry flag obtained in step S610(S620).

For example, if the value of the last entry flag is 1, the value of thecurrent map index idx may be updated to be the same value as the size ofthe palette map of the previous block. In this case, as described above,as the reuse flag is extracted within the size range of the palette mapof the previous block, the reuse flag is not signaled for the paletteentry having the map index value greater than the current map index idx.

On the other hand, when the value of the last entry flag is 0, it meansthat at least one of palette entries having a map index greater than thecurrent map index idx may be reused as a palette entry of the currentblock. Thus, the current map index idx may be increased by one. That is,the current map index idx value is updated to (idx+1), and steps S600and S610 may be repeated until the value of the last entry flag reaches1.

Through the above-described process, the reuse flag of the presentinvention may be limitedly signaled based on the value of the last entryflag.

FIG. 7 illustrates a method of deriving a palette index of a currentblock based on palette index information and a palette index runaccording to an embodiment of the present invention.

First, the process of encoding the palette index information and thepalette index run in the video encoding apparatus will be described. Forconvenience of explanation, it is assumed that that the current block isencoded in the index mode, as shown in FIG. 7, each sample uses apalette index in the range of 0 to 3, and a horizontal traverse scan inwhich the upper-left sample of the current block is the start positionis used.

Referring to FIG. 7, if the palette index used by the current block isarranged in a one-dimensional form according to the horizontal traversescan order, it may be expressed as the following {0, 2, 2, 2, 3, 3, 3,3, 2, 0, 0, 0, 0, 1, 1, 1}. The one-dimensional array may be groupedinto successive and equal-valued palette indices. That is, theone-dimensional array may be composed of a first group consisting of one0 value, a second group consisting of three 2 values, a third groupconsisting of four 3 values, a fourth group consisting of one 2 value, afifth group consisting of four 0 values, and a sixth group consisting ofthree 1 values. The redundancy of the palette indexes for each group isremoved. As shown in Table 1 below, palette index information and/orinformation about the number of palette indices to be encoded may begenerated by specifying and encoding palette indices to be encodedand/or the number of palette indices to be encoded.

TABLE 1 Palette index Palette index Group to be encoded informationPalette index run 1 {0} 0 0 0 2 {2, 2, 2} 2 2 2 3 {3, 3, 3, 3} 3 3 3 4{2} 2 2 0 5 {0, 0, 0, 0} 0 0 3 6 {1, 1, 1} 1 1 2

That is, {0, 2, 3, 2, 0, 1} may be obtained by eliminating theredundancy of the palette index for each group. In this case, thepalette index to be encoded is specified as {0, 2, 3, 2, 0, 1}, and thenumber of palette indices to be encoded may be specified to be six.

In addition, the video encoding apparatus may encode the number of timesthe same palette index is repeated for each group (hereinafter referredto as a palette index run). For example, as shown in Table 1, since thefirst group is composed of one 0 value, the palette index run isdetermined to be 0. In the second group, since the palette index 2 isused at the sample having the scan order (1) and the same paletteindices 2 are successively used at the samples having scan orders (2)and (3), the palette index run may be determined to be 2. The videoencoding apparatus may encode the determined value of the palette indexrun as it is or may divide it into the most significant bit (MSB) andthe refinement bit for encoding efficiency.

Through the above-described process, the video encoding apparatus mayencode at least one of the information about the number of paletteindices to be encoded, the palette index information about the paletteindices to be encoded, or the palette index run.

The video decoding apparatus may obtain the palette index informationand the palette index run from the bit stream and derive the paletteindex for each sample of the current block using the palette indexinformation and the palette index run.

The palette index information may be obtained as many as the numbercorresponding to information on the number of palette indices to beencoded. A palette index run corresponding to each palette indexinformation may be sequentially obtained to derive a palette index ofthe current block. For example, the video decoding apparatus may obtainpalette index information of {0, 2, 3, 2, 0, 1} from the bit stream.Then, a palette index run corresponding to palette index information 0may be obtained from the bitstream. If the value of the palette indexrun corresponding to the palette index information 0 is 0, the videodecoding apparatus may assign the palette index 0 to the sample havingthe scan order (0) of the current block. Then, a palette index runcorresponding to palette index information 2 may be obtained from thebitstream. If the value of the palette index run corresponding to thepalette index information 2 is 2, the video decoding apparatus maysequentially assign the palette index 2 to the samples having the scanorder (1) to (3) of the current block according to the scan order. Inthis way, a palette index may be derived for all samples in the currentblock.

FIG. 8 illustrates a method of deriving a palette index of a currentblock based on palette index information and a palette index run whenthe palette map of the current block is composed of two palette entries.

First, the process of encoding the palette index information and thepalette index run in the video encoding apparatus according to thepresent invention will be described. For convenience of explanation, itis assumed that the current block is encoded in the index mode, twopalette indices are used as shown in FIG. 8, and a horizontal traversescan in which the upper-left sample of the current block is the startposition is used.

Referring to FIG. 8, if the palette indices used by the current blockare arranged in a one-dimensional form according to the horizontaltraverse scan order, it may be expressed the following {0, 0, 1, 1, 1,0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 0, 0}. If the one-dimensional array isgrouped into the palette indices of successive and the same valuesaccording to the method described in FIG. 7 and the redundancy of thepalette indices is removed for each group, the palette indices to beencoded and/or the number of palette indices to be encoded may bespecified.

TABLE 2 Palette index Palette index Group to be encoded informationPalette index run 1 {0, 0} 0 0 1 2 {1, 1, 1} 1 — 2 3 {0} 0 — 0 4 {1, 1,1, 1} 1 — 3 5 {0, 0} 0 — 1 6 {1, 1} 1 — 1 7 {0, 0} 0 — 1

In other words, {0, 1, 0, 1, 0, 1, 0} may be obtained by eliminating theredundancy of the palette index for each group. In this case, thepalette index to be encoded may be specified as {0, 1, 0, 1, 0, 1, 0},and the number of palette indices to be encoded may be specified to be7.

However, when the palette map of the current block is composed of twopalette entries, it is not necessary to encode all the palette indicesto be encoded since two palette indices alternately occur. If only thepalette index of the first sample of the current block (e.g., the samplewith the first scan order) is signaled, the palette index of sampleswith subsequent scan order will be derived in the video decodingapparatus based on the encoded palette index run.

Therefore, in the video encoding apparatus, it is possible to encodepalette index information about the first sample among the paletteindices to be encoded and all palette index runs corresponding to thepalette index to be encoded.

The video decoding apparatus may obtain the palette index informationand the palette index run from the bit stream and derive the paletteindex for each sample of the current block by using the palette indexinformation and the palette index run. Here, as described above, thepalette index information is palette index information about a samplehaving the first scan order in the current block.

Referring to FIG. 8, when the video decoding apparatus obtains paletteindex information 0 from a bitstream and obtains a palette index run 1corresponding to the palette index information, the palette index 0 maybe sequentially allocated to samples having the scan order (1) and (2)in the current block. Then, if palette index runs 2 of a second group isobtained from the bitstream, palette indices of a second group may bederived to be a different value from the palette index used rightbefore. That is, since the value of the palette index used right beforeis 0, the palette index of the second group may be derived to be 1. Inthis case, the video decoding apparatus may sequentially allocate thepalette index 1 to samples having the scanning order (2) to (4) of thecurrent block, in accordance with the scanning order. In this way, apalette index may be derived for all samples in the current block.

FIG. 9 illustrates a scan order used in the palette mode according to anembodiment of the present invention.

Referring to FIG. 9, the scan order used in the palette mode includes ahorizontal scan, a vertical scan, a horizontal traverse scan, and avertical traverse scan.

Specifically, the horizontal scan is a method of scanning each row ofthe current block from left to right, and the vertical scan is a methodof scanning each column of the current block from top to bottom.

The horizontal traverse scan is a method of scanning the odd rows of thecurrent block from left to right and the even rows from right to left. Avertical traverse scan is a method in which odd columns of the currentblock is scanned from top to bottom while an even columns are scannedfrom bottom to top.

However, in this embodiment, it is assumed that the upper-left sample ofthe current block is set to be the scan start position, but the presentinvention is not limited to this, and another corner sample of thecurrent block may be set to be the scan start position.

FIG. 10 illustrates a method of determining the number of paletteentries used by a current block according to an embodiment of thepresent invention.

Referring to FIG. 10, a flag (one_palette_entry_flag) indicating whetherthe number of palette entries used by the current block is 1 may beobtained from the bitstream (S1000).

Specifically, if the value of one_palette_entry_flag is 1, the currentblock is restored using only one palette entry, and if the value ofone_palette_entry_flag is 0, the current block may be restored using aplurality of palette entries. Thus, if the value ofone_palette_entry_flag is 1, the number of palette entries in thecurrent block may be determined to be 1, and if the value ofone_palette_entry_flag is 0, the number of palette entries in thecurrent block is derived based on the number of signaled palette entriesfrom the bitstream.

Referring to FIG. 10, when the value of one_palette_entry_flag is 0, thenumber information (palette_num_signaled_entries) of the signaledpalette entry may be obtained from the bitstream (S1010).

The number information of the signaled palette entries may indicate thenumber of palette entries not included in the previous palette map amongthe palette entries used by the current block.

It is possible to derive the number of palette entries of the currentblock based on at least one of the palette_num_signaled_entries obtainedin step S1010 and the number of palette entries (numPredPreviousPalette)to be reused as palette entries of the current block in the previouspalette map.

Specifically, if the value of numPredPreviousPalette is not 0, thenumber of palette entries of the current block (or the palette size) maybe derived based on the sum of the value of numPredPreviousPalette andthe value of palette_num_signaled_entries (S1020).

On the other hand, when the value of numPredPreviousPalette is 0, itmeans that the palette entry of the previous block is not reused. Thenumber of palette entries of the current block may be derived based onpalette_num_signaled_entries. For example, the number of palette entriesof the current block (or the palette size) may be derived by adding 2 topalette_num_signaled_entries (S1030). This is because if the value ofone_palette_entry_flag is 0, the palette map of the current block willcontain at least two palette entries, so palette_num_signaled_entries isencoded with the number of actual palette entries used by the currentblock minus two. However, the present invention is not limited to this,and palette_num_signaled_entries may be directly encoded as the numberof actual palette entries used by the current block. In this case, thenumber of palette entries of the current block may be derived to havethe same value as palette_num_signaled_entries.

INDUSTRIAL AVAILABILITY

The present invention can be used to code a video signal.

The invention claimed is:
 1. A method of decoding a video signal, themethod comprising: constructing a palette map for a current blockencoded in a palette mode, the palette map comprising at least onepalette entry and a map index that identifies the palette entry;deriving a palette index of the current block on a sample-by-samplebasis; and reconstructing a current sample of the current block by usinga palette entry having a map index of the same value as the derivedpalette index from the palette map, or reconstructing a current samplebased on an escape mode if a value of the palette index relating to thecurrent sample of the current block is equal to the number of paletteentries constituting the palette map of the current block, wherein theescape mode is a method of restoring a sample value based on a signaledpalette escape value, without using a palette entry of the constructedpalette map, wherein the palette entry comprises at least one of apredicted palette entry and a signaled palette entry, the predictedpalette entry means a palette entry reused in the current block amongpalette entries included in a palette map of a previous block, and thesignaled palette entry indicates a palette entry not included in thepalette map of the previous block among the palette entries used by thecurrent block, wherein the predicted palette entry is derived frominformation about palette entry run, the information about palette entryrun is used to determine a number of zeros that precede a non-zero entryin palette entries in the previous block, wherein when a number of thepredicted palette entry is smaller than a maximum number of paletteentry, the signaled palette entry is derived, wherein the palette indexis derived using at least one of an index mode or a copy mode, the indexmode is a method of deriving a palette index based on information aboutpalette index run, and the copy mode is a method of deriving a paletteindex of the current sample using a palette index of a neighboringsample, wherein when at least one sample of the current block uses theindex mode, the palette index is derived using the information aboutpalette index run indicating the number of consecutive sample locationswith same palette index, and wherein a value of the palette index run isentropy encoded selected from one of two encoded types based on a numberof bits used, as a first encoded type, a value of the palette index runis derived from a single encoded element that represents the value ofthe palette index run as is, as a second encoded type, a value of thepalette index run is derived from two encoded elements that represent amost significant bit (MSB) value as is and refinement bits as is of thevalue of the palette index run.
 2. The method of claim 1, wherein theescape mode is adaptively used based on at least one of the number ofpalette entries in a palette map of the current block or a flagindicating whether the current block includes at least one sampleencoded in the escape mode.
 3. A method of encoding a video signal, themethod comprising: constructing a palette map for a current blockencoded in a palette mode, the palette map comprising at least onepalette entry and a map index that identifies the palette entry;deriving a palette index of the current block on a sample-by-samplebasis; and reconstructing a current sample of the current block by usinga palette entry having a map index of the same value as the derivedpalette index from the palette map, or reconstructing a current samplebased on an escape mode if a value of the palette index relating to thecurrent sample of the current block is equal to the number of paletteentries constituting the palette map of the current block, wherein theescape mode is a method of restoring a sample value based on a signaledpalette escape value, without using a palette entry of the constructedpalette map, wherein the palette entry comprises at least one of apredicted palette entry and a signaled palette entry, the predictedpalette entry means a palette entry reused in the current block amongpalette entries included in a palette map of a previous block, and thesignaled palette entry indicates a palette entry not included in thepalette map of the previous block among the palette entries used by thecurrent block, wherein the predicted palette entry is derived frominformation about palette entry run, the information about palette entryrun is signaled to determine a number of zeros that precede a non-zeroentry in palette entries in the previous block, wherein when a number ofthe predicted palette entry is smaller than a maximum number of paletteentry, the signaled palette entry is signaled, wherein the palette indexis derived using at least one of an index mode or a copy mode, the indexmode is a method of deriving a palette index based on information aboutpalette index run, and the copy mode is a method of deriving a paletteindex of the current sample using a palette index of a neighboringsample, wherein when at least one sample of the current block uses theindex mode, the information about palette index run is encoded toindicate the number of consecutive sample locations with same paletteindex, and wherein a value of the palette index run is encoded selectedfrom one of two encoded types based on a number of bits to use, as afirst encoded type, a value of the palette index run is encoded to asingle encoded element that represents the value of the palette indexrun as is, as a second encoded type, a value of the palette index run isencoded to two encoded elements that represent a most significant bit(MSB) value as is and refinement bits as is of the value of the paletteindex run.
 4. The method of claim 3, wherein the escape mode isadaptively used based on at least one of the number of palette entriesin a palette map of the current block or a flag indicating whether thecurrent block includes at least one sample encoded in the escape mode.